Lars magnus ericsson



(fin Model.)

L. M. ERIGSSON. MICROPHONE.

No. 548,748. Patented Oct. 29, 1895;

NITED STATES ATENT' OFFICE.

LARS MAGNUS ERICSSON, OF STOOKHOLM, SWEDEN.

MICROPHONE.

SPECIFICATION forming part of Letters Patent No. 548,748, dated October29, 1895. Application filed July 6, 1895- Serial No. 555,100- (Nomodel.)

To all whom it may concern.-

Be it known that I, LARS MAGNUS Euros- SON, manufacturer, a subject ofthe King of Sweden and Norway, and a resident of Thulegatan 5,Stockholm, in the Kingdom of Sweden, have invented certain new anduseful Improvements in Microphones, of which the following is aspecification, reference being bad therein to the accompanying drawings.

This invention relates to microphones, and has for its object to arrangethem so as to prevent moisture to enter into the microphone-casingthrough the speaking-funnel. Further, the invention has for itsobject'to facilitate the vibrations of the diaphragm.

Figure 1 shows aside view of a microphone arranged according to thisinvention, while Fig. 2 shows a rear side view of the diaphragm.

For preventing moisture, especially the moisture contained in thebreath, from entering beyond the diaphragm in the casing in which thediaphragm and other parts of the microphone are situated-the so-calleddiaphragm-ca singa thin disk Z) is placed in front of the diaphragmathat is to say, between the diaphragm and the speaking-funnel. Theborder of the disk b, as well as that of the diaphragm a, isclose to thewall a of the diaphragm-casing. The disk I), which must be elastic, sothat it can be caused to vibrate in the same way as the diaphragm a, hasno disadvantageous influence upon the microphone in acoustic regard, theeffect of the same being rather the contrary; but if it is properlyarranged and of a suitable quality it completely prevents the moisturefrom entering through the speaking-funnel into the diaphragm-casing orto the diaphragm itself with the breath during the speaking, whichevidently is of great importance for the life of the microphone parts.Specially in carbon-grain microphones it is important to preventmoisture from entering into the diaphragm-casing, because the moisturecauses a bakingtogether of the carbon grains, so that the microphonewill be unserviceable in a relatively short time. It has proved thatcaoutchouc is no suitable material for the disk, as it easily breaks;also, disks made of other materials-for instance, of glimmer-- haveproved less suitable, among other reasons,'because it is necessary tohave a pack ing-ring of caoutchouc at their border, 1n whichring-fissures arise. A suitable material for the disk bis, for instance,silk impregnated with lacquer or another substance, which, when dryafter the impregnation, causes the silk to form solid elastic disks. Theimpregnating material must be of such a nature that it does not becomehard when it has dried, because if it hardens it is liable to crack andbreak, and in such event the moisture is no longer prevented fromentering into the microphone-casing. It is to be observed that in theemployment of these disks it is not necessary to have specialpacking-rings at'their borders, but only to apply so much of theimpregnating material in the forward corner inside the casing that atight joint is obtained round the disk.

The arrangement for facilitating the vibrations of themicrophone-diaphragm consists of the metal plate d, mounted on the rearside of the diaphragm, and the backwardlybent rim of which surrounds thefore part of the soft ring 6 on the carbon block f and serves to preventthe carbon grains from failing out of the said ring e, which latter maybe made of ripped-up felting. This rim of the plate d causes astiffening of the plate, and thus, also, of the middle part of thediaphragm to which the plate is fixed, which stiffening would, if notprovided for, prevent the diaphragm from vibrating with the desireddegree of sensitiveness. For avoiding this inconvenience the plate iscut or slit at the joint between its central portion and its rim alongthe whole length excepting at the points (1', which form the connectionbetween the centralportion and the rim. In this manner the stiffening ofthe plate d by the rim is avoided, which in its turn has for consequencethat the diaphragm can vibrate without hinderance on account of thestiffness of the rim.

Having now described my invention, what I claim as new, and desire tosecure by Letters Patent, is-

1. A microphone comprising the casing, the

vibrating diaphragm and a supplemental pro- ICO 10 cut at the jointbetween the rim and the central portion of the-plate, substantially asdescribed.

In witness whereof I have hereunto signed my name in the presence of twosubscribing witnesses.

'LARS MAGNUS ERICSSON.

Witnesses:

CARL P. GERELL, ERNST SVANGVIST.

